The present invention relates to flexible product packages and. more particularly. to a flexible product package having a resealable closure.
Product packages having reclosure mechanisms arc often employed for packaging products in situations where the consumer may wish to remove only a portion of the product and to reclose the package. Particularly with the current popularity of xe2x80x9cfat-freexe2x80x9d food products, some of which readily dry out if left exposed to atmosphere, there is a significant interest on the part of the product manufacturers in easily and inexpensively produced packaging which can be repeatedly opened and reclosed. Flexible packaging produced from flexible sheet materials are generally favored for reasons of cost, functionality, and marketing appeal.
Various types of reclosure mechanisms have been developed for reclosing, a flexible package to keep unused portions of a food product fresh. Many of these mechanisms are separately manufactured articles which arc added to the package either in a subsequent manufacturing step or by the consumer, such as zippers, reclosure tapes or tabs, seal strips. clips, and the like. However, such mechanisms are disadvantageous because they necessitate additional manufacturing operations and materials, thus increasing manufacturing cost. Accordingly, efforts have been made toward developing adhesive-based reclosure mechanisms for flexible packages, since such packaging is readily produced on automated flexible web-handling machinery and does not require additional components such as zippers or the like.
The challenge in making a reclosure mechanism which relies on adhesive for resealing is that an adhesive which may be suitable for forming the original package seal, which must have sufficient strength and integrity to prevent inadvertent opening of the package and to keep the product fresh during handling and shipment, is generally different from the type of adhesive which is desirable from a resealing point of view. Cold seals, hot-melts, and heat seals provide good seal strength and are thus suitable for forming original package seals. Unfortunately, such materials do not generally provide sufficient reclosure capabilities. Pressure-sensitive adhesives can be repeatedly removed and reattached to suitable substrates and thus can provide reclosure capabilities. However, pressure-sensitive adhesives do not provide sufficient closure strength to form reliable original package seals in many applications. Furthermore, because pressure-sensitive adhesives are inherently tacky and will stick to almost any surface they come in contact with, automated handling of sheets or webs to which pressure-sensitive adhesives have been applied is difficult. For example, the pressure-sensitive adhesive may become stuck to the rollers of an apparatus, a problem known in the industry as xe2x80x9cpicking.xe2x80x9d Additionally, the web may stick to itself when it is wound into a roll and stored prior to being used, a problem known as xe2x80x9cblocking.xe2x80x9d
Accordingly, pressure-sensitive adhesives are commonly used in conjunction with backing layers of paper or other material to which a release coating has been applied, as shown in U.S. Pat. No. 3,827,625. When it is desired to operate a seal employing such a pressure-sensitive adhesive mechanism, the backing layer is removed to expose the pressure-sensitive adhesive, and the pressure-sensitive adhesive is pressed against a cooperating part of the package to effect a closure, whether an original seal or a reclosure of a previously opened seal. Alternatively, the backing layer is permanently attached to the cooperating part of the package to effect an original seal, and the substrate which carries the pressure-sensitive adhesive is peeled from the backing layer to open the original seal. as shown in U.S. Pat. No. 3,272,422. In either case, reclosure is effected by pressing the pressure-sensitive adhesive against the cooperating part or the backing layer.
The disadvantages of such closure mechanisms are that additional material and manufacturing operations are required to form the backing layer, and the strength of the original seal is only as good as the strength of the pressure-sensitive adhesive, which as previously noted is insufficient in many cases.
The assignee of the present application has previously developed a reclosure mechanism for a flexible package, as disclosed in co-pending U.S. patent application Ser. No. 09/203,269. which is incorporated herein by reference. The ""269 application describes a package having, a re-sealable seal formed by a layer of pressure-sensitive adhesive applied to the inner surface of one portion of the packaging sheet adjacent an edge thereof. and a layer of a cohesive material such as a cold seal or heat seal applied over the pressure-sensitive adhesive and over a surface of an opposing portion of the sheet that is placed in contact with the one portion and sealed thereto to form a package seal. When the seal is first opened. the pressure-sensitive adhesive detaches from the one portion of the sheet so that it is attached to and exposed on the opposing portion of the sheet. The package is reclosed by pressing the two portions together to cause the pressure-sensitive adhesive to stick to the one portion. The ""269 application further describes that a second seal may be formed immediately adjacent to the edge of the sheet outward of the re-sealable seal so as to improve the strength of the original package seal along this edge. The second seal is formed by a strip of the cohesive material applied to the inner surface of the sheet without the interposition of any pressure-sensitive adhesive facing portions of the sheet being sealed together along the edge via this strip of cohesive.
The present invention was developed to further improve upon the package disclosed in the ""269 application, with a particular emphasis being to provide a package especially suitable for vertical form, fill, and seal (VFFS) applications. Where a cold seal material is used for forming the re-sealable seal and second seal in the package of the ""269 application, the seals do not develop their full strength immediately upon sealing, but rather can take a substantial amount of time, tip to several hours, before they reach their full strength. Immediately after sealing, these seals tend to be fairly weak, and thus may not be capable of withstanding the forces exerted on them in a VFFS packaging operation, where the weight of the package contents bears upon the seal when the package is filled. Cold seal materials also tend to be tacky and will not flow freely through VFFS machines. The present invention was developed to address these problems.
In accordance with a preferred embodiment of the present invention, a package having a re-sealable seal is formed from a flexible sheet having its opposite longitudinal edge portions sealed together to form a tubular structure with a permanent longitudinal seal extending lengthwise therealong. Two opposite permanent end seals are formed transversely across the tubular structure to seal the product inside the package. At one end of the package, a re-sealable seal is formed adjacent the permanent end seal. In this embodiment, the package is opened at the end of the package having the re-sealable seal. The re-sealable seal is formed by a pressure-sensitive adhesive applied to a first region of the inner surface of the sheet proximate the end seal and a heat seal coating applied over the pressure-sensitive adhesive so as to cover the pressure-sensitive adhesive, and a heat seal coating applied over a second region of the inner surface of the sheet. The first and second regions of the inner surface are placed in contact with each other and have the heat seal coatings thereon sealed together so as to form the re-sealable seal.
In an alternative embodiment of the invention, the re-sealable seal is formed so as to extend longitudinally along the package adjacent to the permanent longitudinal seal. In this embodiment, the package is opened along the longitudinal seal.
The heat seal coating provides a relatively strong seal immediately upon sealing. This is advantageous particularly for VFFS applications where the resealable seal is at one end of the package such that the weight of the package contents bears upon the seal. In a preferred embodiment of the invention. the sheet""s inner surface comprises a heat-sealable material. The sheet can comprise a lamination of more than one layer, the inner layer comprising a heat-sealable material. Alternatively, heat seal coatings can be applied to the inner surface of the sheet for making the permanent heat seals. The permanent seals are formed by heat sealing via the heat-sealable material on the inner surface. Preferably, the seal coating covering the pressure-sensitive adhesive is also a heat seal coating. Accordingly the permanent seal and the adjacent re-sealable seal can both be formed by heat sealing, and advantageously can be formed simultaneously during a packaging operation.
In accordance with a particularly preferred method of the invention, which can be used in VFFS and other applications, a continuous web of the sheet material is advanced and a leading portion of the advancing web is folded and has its longitudinal edge portions sealed together to form a tubular structure. A transverse seal is formed across the tubular structure to form a first end seal for a package and the product is placed into the package before or after the first end seal is formed. A second end seal on the opposite end of the package is then formed along with the re-sealable seal, and the resulting package is severed from the remainder of the web. Advantageously, the first end seal for one package and the second end seal and re-sealable seal for the adjoining package can be formed simultaneously.
In an alternative method embodiment of the invention, the web is advanced and is folded into a tubular shape, and the opposite longitudinal edges are sealed together with both a permanent seal and an adjacent re-sealable seal having the construction described above. One permanent end seal is formed transversely across the package, and the contents are placed in the package, and the opposite permanent end seal is formed and the package is severed from the rest of the web.
Preferably, the package and method of the invention also include the formation of an easy-open feature located between the permanent seal and the adjacent re-sealable seal, enabling the package to be easily opened to gain access to the contents. In a preferred embodiment of the invention. the easy-open feature enables the part of the package having the permanent seal to be torn off the package so that the re-sealable seal is all that remains for sealing the package)e opening. The consumer can then open the re-sealable seal, remove a portion of the contents, and reclose the package by operating the re-sealable seal. Alternatively, the easy-open feature may create an opening through the sheet to enable the user to then open the re-sealable seal without tearing the permanent seal from the package. The easy-open feature may comprise a perforation, a tear strip, a mechanically formed or laser-formed scoreline, or the like.